Prime power and space saving are also achieved. The category of oscillators based on long optical delay lines to provide high frequency stability 29 is known as OEO. Narrowband filters are the core part of an OEO, determining the oscillation frequency by employing extremely narrowband fixed frequency filters. Removing them is not feasible, even using narrowband electronic filters.
Coarse tuning of a wideband YIG filter 36 combined with fine tuning a narrowband wavelength-tuned optical transversal filter using short delay lines or a chirped fiber Bragg grating 44 provides high resolution frequency selectivity. Nonetheless, a number of side-modes persist, although forced oscillation techniques can reduce the oscillation side-modes.
The benefits of ILPLL 25 in electronic systems 45 are from improvements in close-in phase noise, pull-in time and the locking and tracking ranges, compared to the standard IL or PLL, and reduced prime power and space compared to a multiplier chain. This article focuses on the development of a self-forced OEO and is presented in two parts. Part 1 discusses the design and testing of a 19 in.
Computer control generates both FMCW and frequency hopped operation of the synthesizer, enabling it to be used for remote sensing and secure communications applications. In Part 2 of the article, additional design innovations are described which lead to a compact OEO.
The block diagram of the OEO synthesizer is shown in Figure 1. The laser signal transmits through optical fiber delay lines and is received by high speed photodetectors Discovery Semiconductors DSC50S to generate an electrical signal which passes through a narrowband filter. This narrowband filter is the core of the OEO, used to select the oscillation frequency. A high Q metallic filter is the classic approach to realize a fixed frequency OEO, where mechanical adjustment of the cavity length tunes the frequency.talrenn.tk
Comb-rooted multi-channel synthesis of ultra-narrow optical frequencies of few Hz linewidth
As this approach is not suitable for computer control, a YIG filter 36 is used for this synthesizer design. The YIG filter is attractive because it has a broad tuning range and can be computer-controlled. To compensate for the poorer frequency selectivity of wide-tuning YIG filters, a narrowband optical transversal filter 42 is added, realized with a 30 m fiber.
The YIG filter provides coarse tuning of the synthesizer, i. The highest resolution for the power supply Keysight EA in constant current mode is 1 mA, so smaller frequency steps will be provided by the transversal filter. Figure 2 First-order optical transversal filter using a 3 dB splitter and combiner with an optical delay in one path.
An optical transversal filter 42 can provide narrowband filtering of microwave signals; a first-order transversal filter is shown in Figure 2. An optical signal is divided into two paths, with one path the reference, the other creating the delay. This is represented by the following filter transfer function, in terms of RF frequency.
Figure 3 View of the custom fiber mandrels adjacent to the computer-controlled DC power supply. Figure 4 View of the fiber laser source, driver and commercial YIG filter. The null-to-null bandwidth is around 4. Using computer control, after setting the desired frequency, the frequency setting process terminates when the difference between the desired frequency and the detected frequency is smaller than half the fine tuning resolution, approximately 10 kHz; the final output is then shown on the LabVIEW display.
A double balanced mixer is integrated on the same board with a lowpass filter amplifier, realized with op-amp circuits, which serves as the phase detector and lowpass filter portion of the PLL. Figure 5 View of the RF and fiber-optic components on the third level of the synthesizer housing. Figure 6 Front view of the OEO synthesizer, showing the power supply left , 1 and 5 km fiber mandrels, laser driver and other components. After successfully demonstrating the synthesizer on a lab table, it was integrated into a 19 in.
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The assembly detail is shown in the following views, where the step-by-step assembly of the system reflects the block diagram shown in Figure 1. The first floor of the synthesizer box see Figure 3 comprises three fiber mandrels and the DC power supply. The topside of the cover over the mandrels and power supply contains the laser driver, laser and YIG filter see Figure 4 , commercial products from Optilab and Teledyne. Figures, Tables, and Topics from this paper.
Figures and Tables.
References Publications referenced by this paper. Nanometer frequency synthesis beyond phase-locked loop Liming Xiu. Low-noise low-power design for phase-locked loops Feng R. Zhao , Fa Foster Dai.
Enhanced phase-locked loop structures for power and energy applications Masoud Karimi-Ghartema. Time-to-Digital Converters Stephan Henzler. High-speed analog-to-digital conversion Michael J. Frankle , Peter Atkinson.